The Stovebolt Site Forums The Shop Area Driveline Changing a 4.10 to 3.73 - appears pretty simple

You just never know what you'll see at a swap meet. I was walking around last weekend, this fella had 1/2 dozen rear-ends he was working on for folks at the meet. 3 sockets 5/16, 5/8 and 1 1/4 (I think) and he changed out the R/P and had a 3.73 in about 20 minutes. He works out of his house, so any folks around Houston interested, let me know.

I think I could outrun somebody who tried to give me one of those rear ends! I've been setting up gearsets for a little over 50 years and anybody who tries to set a speed record swapping gears is not your friend!
Jerry

But if you have everything handy, obviously these were out of the vehicles, is that a reasonable amount of time...or are there critical steps he may have left out?

Usually in setting up a ring and pinion requires a dial indicator and a marking substance to check gear tooth contact. It take some careful attention for a quiet running differential.
He wasn't just changing carriers was he??

John

No John, he pulled the diff case out, both shafts backed out the pinion...and put it all back. I've never seen anyone do it, but looks like something my local shop would charge me an arm and a leg to do. Apparently he does a fair amount of business from these swap meets, and word gets around fast about knuckleheads. I didn't see a dial indicator or marking substance? At what stage do you need to do it?

I need an inch-pound torque wrench to set up the pinion bearing preload, a dial indicator for backlash, a shim pack and indicator dye for setting the tooth contact pattern, and all new bearings for the pinion and the carrier. An arbor press, a bearing splitter, and a couple of gear pullers are almost a necessity. I've done some quick and dirty gear changes in the pits of a race track, once lying under the car on 120-degree asphalt, but I was not the least bit concerned with reliability, gear noise, or even getting further than taking the checkered flag in a few minutes. (We won the race, BTW!)

Doing a sloppy setup on a street-driven gearset is just wrong in so many ways! I'd be ashamed to take advantage of anybody like that!
Jerry

Is he simply unbolting one carrier assembly and installing one with a different ratio? I could understand that being a 20-30 minute job, but swapping the ring and pinion into a carrier would take more like 2-3 hours to do it right, and a lot more equipment than the average swap meet vendor would have at his disposal.
Jerry

He clearly took some shortcuts. Maybe better to just have him locate a 3.73 rear end that would bolt up. Once saw an F150 facing the wrong way on a 5 lane interstate, missing one rear wheel with axle intact...which was a hundred yards further down on the shoulder. Can you imagine what that would feel like at 70 mph ! Have to be careful not to gold plate every possible aspect on these restorations!

Jerry, you need to find a way to get some of those old racing pictures up on the net. Also, what is the reduction in rpm's, if all else is the same. Is it (4.10/3/73-1) or 10% reduction ?

What are you trying to swap a differential in? I've heard of the Ford's losing an axle also.....

John

My 48 3600 has that low low 4 speed and rear end combination. I was thinking I would leave the 4 speed, use it as a 3 speed most of the time, and convert the rear end to 3.73 at least. I like that big ole 4 speed on the floor, it's just geared so low.

My 59 Burb ended up with a 3/4 ton Dana type 60 from a GMC, with a set of 3.73 gears from a Ford in it. A friend gave me the rear end, with a broken pinion gear and the input yoke missing. I scavenged up a bunch of junkyard parts, and ended up with a GMC housing, Ford gears, and a Dodge pinion flange. I could have also used some International parts, since all those trucks used Dana rear ends. The front axle is still the original 6-lug Chevy 1/2 ton for now, but I'm getting ready to put an early 80's Chevy 3/4 ton disc brake front suspension under it, with the crossmember narrowed about 3" to fit the 59 frame.
Jerry

I'm not sure if there is a 3.73 ratio available for those or not. There have been some threads saying later 3/4 ton rear ends can be swapped in place of the original. I believe most of those are 4.10's. The original is either 4.57 or 5.14....

John

As I read this thread, the answer is not complete. As far as I knew the ring and pinion much less than 4.10s were not able to fit an HO52 or HO72 pumpkin.

I think it's entirely possible the original post was referring to car rear ends, not trucks. I ran a 3.55 and a 3.70 gear at various times in a 58 Chevy car, and those rear ends interchanged from 55 to 64. They DO NOT fit the truck housing. Dana/Spicer rear axles with the non-removable center housing were used in some GMC applications, Ford, Dodge, and International trucks, as well as several Ford car applications. The one I swapped into my 59 Burb was a mid-1970's GMC axle with a limited-slip Dana type 60 gear.
Jerry

The Spicer/Dana 60 also saw use in Plymouth and Dodge Passenger cars, mostly in cars equipped with the 426 Hemi (it was a required option with the Hemi/4 speed), though some 440 cars had them, too.